Method and apparatus for continuously measuring the concentration of a reactant in a liquid carrier

ABSTRACT

The concentration of a reactant in a liquid carrier is continuously determined by continuously mixing the carrier with another one containing a reactant capable to react with the tested reactant under gas generation, and by continuously measuring changes in either the overall specific gravity of the resulting gas/liquid mixture, or the overall electrical conductivity of the mixture. Suitable simple apparatus is shown.

United States Patent Ludvikt 51 Mar. 28, 1972 [54] METHOD AND APPARATUSFOR 56] References Cited CONCENTRATION OF A REACTANT IN STATES PATENTS3,018,654 1/1962 Gordon et al ..73/23 A LIQUID CARRIER Appl. No.:847,546

[1.8. CI. ..23/230 R, 23/253 R, 73/401, 73/438, 324/30 Int. Cl. ..G0ll7/18, G01n 9/26, G0ln 27/10 Field of Search ..23/230, 253; 324/30 B;73/438, 73/401 3,468,764 9/ 1969 Cohen et a1 3,527,571 9/1970Neubergeretah ..23/253 Primary Examiner-Morris O. Wolk AssistantExaminer-R. M. Reese AttorneyRichard Low [57] ABSTRACT tivity of themixture. Suitable simple apparatus is shown.

12 Claims, 2 Drawing Figures PATENTEDMAR28 I972 @NVENTOR METHOD ANDAPPARATUS FOR CONTINUOUSLY MEASURING THE CONCENTRATION OF A REACTANT INA LIQUID CARRIER BACKGROUND OF THE INVENTION This invention relates tocontinuous analysis of process streams, and more particularly to thedetermination of a constituent of such a stream which is capable ofgenerating a gas in a stoichiometric ratio when interacting with asuitable reagent.

Hydrogen peroxide is a common constituent of textile bleaching liquors.It has been determined quantitatively in such liquors heretofore bytitration in an acid medium with potassium permanganate solution. Thetitration is relatively time consuming, cannot be fully automatedwithout the use of very complex equipment, and the results of thetitration cannot readily be converted into signals suitable forcontrolling the peroxide concentration in the bleaching liquor.Moreover, relatively large amounts of the expensive permanganatestandard solution are needed.

The primary object of this invention is the provision of an analyticalmethod for determining the concentration of hydrogen peroxide inbleaching liquor which is simple and inexpensive, permits continuoussampling of the liquid in a bleaching tank, and may provide controlsignals for keeping the concentration of hydrogen peroxide in the tankpractically uniform.

Another object is the provision of apparatus for performing the method.

With these and other objects in view, as will hereinafter becomeapparent, the method of the invention involves the continuousindependent feeding of first and second liquid carriers at respectiveconstant first and second rates to a reaction vessel having an overflow,first and second reactants, such as hydrogen peroxide and an oxidizingagent, being respectively dissolved or dispersed in the carriers. Thereactants are selected for their ability of reacting with each other inthe resulting mixture of the carriers and of forming reaction productsincluding a gas which is formed by the reaction at a rate proportionalto the concentration of the first reactant in the first carrier. Thesecond rate must be high enough to maintain in the vessel an excess ofthe second reactant. The carriers should be miscible, and the gas formedat least partly insoluble in the mixture of the carriers. When theresulting gas/liquid reaction mixture is continuously permitted to bewithdrawn by overflow from the reaction vessel at a third ratesufficient to keep the combined volume of the reactants, the carriers,and the reaction products in the vessel substantially constant, aphysical property of the mixture in the vessel may be measured as anindication of the concentration of the gas present in the mixture as adispersed separate phase. The measurement is thus uniquely related tothe initial concentration of the first reactant in the first carrier.

Suitable apparatus for performing the method may include an uprightreaction tube having an opening at the top, feeding means for separatelyfeeding the carriers to the bottom portion of the reaction tube for flowof the resulting reaction mixture from the bottom portion to the topportion of the tube to be withdrawn outward of the tube through theopening. A manometer arrangement may then measure the hydrostaticpressure in the bottom portion of the tube as an indicator of theconcentration of the first reactant in the first carrier.

Alternatively, the carriers may be fed to the bottom of the reactiontube through two conductivity cells, the cells and the tube beingequipped each with a pair of spaced electrodes, and the electrodesconnected in a bridge circuit for measuring the changes in electricalconductivity of the reaction mixture in the reaction tube' Otherfeatures, additional objects, and many of the attendant advantages ofthis invention will readily be appreciated as the same becomes betterunderstood by reference to the following description of preferredembodiments when considered in connection with the appended drawing.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 shows apparatus for analyzing a bleaching liquor containinghydrogen peroxide by measuring the hydrostatic pressure of a reactionmixture of the liquor with a sodium hypochlorite solution, the apparatusbeing shown in side elevation; and

FIG. 2 illustrates apparatus for analyzing the aforementioned liquor bymeasuring the overall electrical conductivity of the aforementionedreaction mixture, the view being as in FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring initially to FIG. 1,there are shown the two supply conduits 1, 2 of two commonly drivenpositive displacement pumps, not otherwise shown, such as twoperistaltic pumps whose rotors are mounted on a common drive shaft. Theconduits 1,2 are joined to an inlet tubulure of an upright, cylindricalreaction tube 3. A flexible hose 4 connects the lower end of the tube 3to one end of a measuring tube 5 of uniform bore. A scale 6 attached tothe tube 5 is calibrated in units of length along the axis of the tube5, as will presently be described in more detail.

The end of the tube 5 remote from the hose 4 communicating with ambientatmosphere is attached to an upright supporting plate 24 by a pivot pin7 having a horizontal axis on the same level as the upper end of thereaction tube 3 which is surrounded by an overflow vessel 8 equippedwith a drain 9 for withdrawal of fluid. The friction in the pivot issufficient to hold the tube 5 in the angular position in which it is setby hand. The zero point of the scale 6 coincides with the pivot axis andis not affected by angular movement of the tube 5.

A fixed electrode 11 in the metering tube 5 adjacent the hose 4 and anelectrode 10 axially entering the tube 5 through a loosely fitting plug25 near the pivot pin 7 are connected to respective terminals 26 and 27on the plate 24. The upper end of the metering tube 5 is then open toatmosphere due to loosely fitting plug 25.

The apparatus shown in FIG. 1 is operated as follows:

The nonillustrated; ganged,. positive displacement pumps arerespectively connected to a bleaching tank and to a reagent supplyvessel for pumping bleaching liquor containing hydrogen peroxide and alarge excess of sodium hypochlorite solution at respective constantrates into the reaction tube 3 where the hydrogen peroxide is decomposedalmost instantaneously to water and oxygen gas. The reaction mixturerises in the tube 3 and overflows from the open top of the tube into thevessel 8 and flows into waste through the drain 9, to maintain thecombined volume of the reactants, the carriers and reaction products inthe vessel substantially constant.

At a constant pumping rate and otherwise reasonably uniform conditions,the amount of oxygen dispersed in bubbles in the liquid flowing throughthe reaction tube 3 is a unique function of the hydrogen peroxidecontent of the bleaching liquor. When the liquor or sodium hypochloritesolution contains a small amount of surfactant or wetting agent, theoxygen bubbles in the flowing liquid are too small to travel upwardly ata significantly higher rate than the enveloping liquid, and they do notadhere to the walls of the tube.

The reaction tube 3 and the measuring tube 5 communicate through thehose 4. In pumping the sodium hypochlorite solution and, into thereaction tube initially, the level thereof in the measuring tube remainsaligned with the overflow edge of the reaction tube. The difference inspecific gravity between bleaching liquor and the sodium hypochloritereagent solution isinsignificant, so that when afterwards the bleachingliquor is pumped into the reaction tube simultaneously, as described,changes in the liquid level in the wetting tube correspond to thechanges of the hydrostatic pressure in the bottom portion of the tube 3or of the specific gravity of the reaction mixture in the reaction tube3, depending on the amount of oxygen dispersed in the tube 3. The scale6 may be calibrated directly in grams of active oxygen per liter ofbleaching liquor or in similar units.

If the characteristics of the system are changed, for example, afterreplacement of a resilient tube in the peristaltic pump supplying thebleaching liquor or the reagent solution or by major changes in ambienttemperature of pressure, the

measuring tube 5 is reset angularly on the pivot pin 7 to restore propercalibration.

The illustrated apparatus may also control the supply of hydrogenperoxide to the bleaching tank in order to make up for consumption ofthe oxidizing agent and for drag-out losses. The terminals 26, 27 arearranged in a nonillustrated; and entirely conventional circuit with arelay, a current source and a normally closed solenoid valve in a supplyline connecting a storage vessel for hydrogen peroxide with thebleaching tank.

When the peroxide content in the liquor pumped to the reaction tube 3decreases, the specific gravity of the liquid in the reaction tubeincreases and the level of the gas-free liquid in the measuring tube 5rises. The liquid in the tube 5 is sufficiently conductive to energizethe relay when the liquid connects the electrodes 10,11, and the relaycloses the energizing circuit of the solenoid valve to supply freshhydrogen peroxide to the bleaching tank. The resulting gradual increasein the gas content and decrease in the specific gravity of the liquid inthe reaction tube 3 causes the liquid level to fall in the measuringtube 5 until the circuit between the electrodes 10,11 is broken,.and thenon-illustrated solenoid valve interrupts the flow of oxidant to thebleaching tank. The hydrogen peroxide concentration in the bleachingliquor may be changed by shifting the electrode 10.

The illustrated apparatus may be used without change for measuringhypochlorite concentration in an alkaline chlorine bleaching liquor whenhydrogen peroxide in excess is used as the reagent. The scale 6 may becalibrated in grams of available chlorine per liter of bleaching liquidor similar units.

The apparatus shown in FIG. 1 combines simplicity with good sensitivity,and has been operated successfully over extended periods. It needs to becleaned periodically from gross contaminants carried over from thebleaching tank, but does not require any other maintenance work. It maybe modified, if so desired, by substituting any other type of indicatingand controlling manometer for the tube 5 and its electrodes 10,11.

The analyzer shown in FIG. 2 has an upright reaction tube 3 whose opentop is received in an overflow vessel 8 equipped with a drain 9, asdescribed above. The lower end of the reaction tube 3 is connected by aY-fitting with two conductivity cells 12,13 which are open-ended tubesequipped with respective pairs of axially spaced electrodes 14,15 and16,17. Two electrodes 18,19 are similarly spaced axially in the reactiontube 3.

A proportionating pump 21, which may consist of two ganged peristalticpumps as described above, is arranged to pump bleaching liquorcontaining hydrogen peroxide from a non-illustrated bleaching tankthrough one of the cells 12,13 into the reaction tube 3, and sodiumhypochlorite reagent solution from a non-illustrated storage vesselthrough the other cell into the reaction tube 3' where the two liquidsare mixed at fixed rates and oxygen bubbles are formed by the reactionof hydrogen peroxide and sodium hypochlorite.

The electrodes 14 19 are connected with each other, with a potentiometer20, a galvanometer 23, and an alternating current source in a resistanceor conductivity bridge circuit. The electrodes of the two cells 12,13are arranged in parallel circuit in one arm of the bridge circuit, andthe electrodes 18,19 in the reaction tube 3 provide the second arm. Theportions of the potentiometer 20 between the two fixed terminalsrespectively and the movable terminal provide the third and fourth armsof the bridge. The current source 28 is connected across one diagonal ofthe bridge, and the galvanometer 23 equipped with a rectifier 22 isconnected across the other diagonal, as is conventional.

Conductivity changes in the two pumped liquids do not affect thereadings of the device illustrated in FIG. 2 which indicate thedistribution of liquid and gas in the fluid flowing through the reactiontube 3'. At a constant pumping rate, and in the presence of a largeexcess of the reagent over the analyzed compound, the readings of thebridge circuit are uniquely related to the variable concentration of theanalyzed compound which may be read from a nonillustrated;experimentally calibrated scale cooperating with the movablepotentiometer contact when the galvanometer 23 reads zero. The apparatusshown in FIG. 2 may be modified in an obvious and well-known manner tocontrol the flow of hydrogen peroxide or of sodium hypochlorite solutionto a bleaching tank in the manner of the device illustrated in FIG. 1.

The apparatus illustrated in FIGS. 1 and 2 may be employed to measurethe quantitative relationship of a known liquid and a gas dispersed inthe liquid as a separate phase regardless of the reaction which producesthe mixture of gas and liquid, and may thus be employed for measuringthe concentration of reagents other than those specifically describedwith reference to the drawing. Potassium permanganate and other solublesalts of hypochlorous acid such as the calcium salt may be substitutedfor the sodium hypochlorite in a known manner for determining theconcentration of hydrogen peroxide or of the permanganate or calciumhypochlorite, and other reactants will readily suggest themselves tothose skilled in the art.

While aqueous carriers for the reactants have been describedspecifically, at least the apparatus of FIG. 1 may be employed withoutchange for measuring concentration of the gas-generating reactant in anon-aqueous liquid carrier. The gas produced must be at least partlyinsoluble in the reaction mixture, but the carriers should be misciblewith each other, and the physical property that is measured is afunction of the amount of gas dispersed as a separate phase in thereaction mixture.

I claim:

1. A method of continuously measuring the concentration of a firstreactant in a first liquid carrier which comprises:

a. continuously feeding said first liquid carrier containing said firstreactant to a reaction vessel at a constant first rate;

b. continuously feeding separately a second liquid carrier having asecond reactant dispersed therein to said reaction vessel at a constantsecond rate, whereby a mixture of said carriers and said reactants isformed in said vessel,

1. said reactants being capable of reacting with each other in saidmixture and of forming reaction products including a gas formed by thereaction at a rate proportional to the concentration of said firstreactant in said mixture,

2. said second rate for feeding said second liquid carrier beingsufficient to maintain in said vessel an excess of said second reactant,

3. said carriers being miscible, and said gas being at least partlyinsoluble in the mixture of said carriers,

continuously permitting the flow of reaction mixture from said reactionvessel at a third rate sufficient to keep the combined volume of saidreactants, of said carriers, and of said reaction products in saidvessel substantially constant; and

. continuously measuring a physical property of the reaction mixture insaid vessel as an indication of the concentration of said gas present insaid mixture as a dispersed separate phase. v

2. A method as set forth in claim 1, wherein said physical property isthe overall specific gravity of said reaction mixture.

3. A method as set forth in claim 1, wherein said physical property isthe overall electrical conductivity of said reaction mixture.

4. A method as defined in claim 1, wherein at least one of said liquidcarriers contains a wetting agent.

5. A method as set forth in claim 1, wherein one of said reactants ishydrogen' peroxide, said gas is oxygen, and said carriers are aqueousliquids.

6. A method as set forth in claim 5, wherein the other reactant is asoluble salt of hypochlorous acid.

7. An apparatus suitable for measuring hydrogen peroxide concentrationin an aqueous bleaching bath comprising, in combination:

a. an upright reaction tube having a top portion and a bottom portion,said top portion having an opening;

b. feeding means for separately feeding said bath and a reagent solutionto said bottom portion for flow of the resulting mixture from saidbottom portion to said top portion and outward of said tube through saidopening; and

c. manometer means for measuring the hydrostatic pressure in said bottomportion.

8. An apparatus as defined in claim 7, wherein said manometer meansincludes a pressure measuring tube communicating by one of its ends withthe ambient atmosphere and by the other end with the bottom portion ofsaid reaction tube, said reaction tube and said pressure measuring tubeforming communicating vessels; and comprising index means for indicatingchanges in liquid level in said pressure measuring tube.

9. An apparatus as defined in claim 8, wherein the liquid in saidpressure measuring means is electrically conductive, and wherein astationary electrode is mounted in said pressure measuring tube at itsend adjacent the bottom of said reaction tube, and an adjustableelectrode is arranged in said pressure measuring tube at its other end.

10. An apparatus as defined in claim 8, wherein said pressure measuringtube communicates with the bottom portion of said reaction tube via aflexible hose and is pivotally mounted at its upper part for changingthe slant and thus the response thereof.

11. An apparatus suitable for measuring hydrogen peroxide concentrationin an aqueous bleaching bath comprising, in combination:

a. an upright reaction tube having a top portion and a bottom portion,said top portion having an opening;

b. two tubular cells having each a first and a second end portion, saidfirst end portions communicating with said bottom portion;

c. means for feeding said bath and a reagent solution to said second endportions respectively for flow through said cells into said reactiontube, and for discharge of the resulting mixture from said tube throughsaid opening;

d. a pair of spaced electrodes in said reaction tube and in each of saidcells; and

e. bridge circuit means conductively connecting said elec trodes formeasuring the difference between the conductivity of the mixture in saidtube and the combined conductivity of said bath and of said reagentsolution in said cells.

12. An apparatus as defined in claim 1 1, wherein said bridge circuitmeans is a Wheatstone bridge circuit.

2. A method as set forth in claim 1, wherein said physical property isthe overall specific gravity of said reaction mixture.
 2. said secondrate for feeding said second liquid carrier being sufficient to maintainin said vessel an excess of said second reactant,
 3. said carriers beingmiscible, and said gas being at least partly insoluble in the mixture ofsaid carriers, c. continuously permitting the flow of reaction mixturefrom said reaction vessel at a third rate sufficient to keep thecombined volume of said reactants, of said carriers, and of saidreaction products in said vessel substantially constant; and d.continuously measuring a physical property of the reaction mixture insaid vessel as an indication of the concentration of said gas present insaid mixture as a dispersed separate phase.
 3. A method as set forth inclaim 1, wherein said physical property is the overall electricalconductivity of said reaction mixture.
 4. A method as defined in claim1, wherein at least one of said liquid carriers contains a wettingagent.
 5. A method as set forth in claim 1, wherein one of saidreactants is hydrogen peroxide, said gas is oxygen, and said carriersare aqueous liquids.
 6. A method as set forth in claim 5, wherein theother reactant is a soluble salt of hypochlorous acid.
 7. An apparatussuitable for measuring hydrogen peroxide concentration in an aqueousbleaching bath comprising, in combination: a. an upright reaction tubehaving a top portion and a bottom portion, said top portion having anopening; b. feeding means for separately feeding said bath and a reagentsolution to said bottom portion for flow of the resulting mixture fromsaid bottom portion to said top portion and outward of said tube throughsaid opening; and c. manometer means for measuring the hydrostaticpressure in said bottom portion.
 8. An apparatus as defined in claim 7,wherein said manometer means includes a pressure measuring tubecommunicating by one of its ends with the ambient atmosphere and by theother end with the bottom portion of said reaction tube, said reactiontube and said pressure measuring tube forming communicating vessels; andcomprising index means for indicating changes in liquid level in saidpressure measuring tube.
 9. An apparatus as defined in claim 8, whereinthe liquid in said pressure measuring means is electrically conductive,and wherein a stationary electrode is mounted in said pressure measuringtube at its end adjacent the bottom of said reaction tube, and anadjustable electrode is arranged in said pressure measuring tube at itsother end.
 10. An apparatus as defined in claim 8, wherein said pressuremeasuring tube communicates with the bottom portion of said reactiontube via a flexible hose and is pivotally mounted at its upper part forchanging the slant and thus the response thereof.
 11. An apparatussuitable for measuring hydrogen peroxide concentration in an aqueousbleaching bath comprising, in combination: a. an upright reaction tubehaving a top portion and a bottom portion, said top portion having anopening; b. two tubular cells having each a first and a second endportion, said first end portions communicating with said bottom portion;c. means for feeding said bath and a reagent solution to said second endportions respectively for flow through said cells into said reactiontube, and for discharge of the resulting mixture from said tube throughsaid opening; d. a pair of spaced electrodes in said reaction tube andin each of said cells; and e. bridge circuit means conductivelyconnecting said electrodes for measuring the difference between theconductivity of the mixture in said tube and the combined conductivityof said bath and of said reagent solution in said cells.
 12. Anapparatus as defined in claim 11, wherein said bridge circuit means is aWheatstone bridge circuit.